Field ot the Invention
The invention relates generally to in circuit emulators and more particularly to emulators for in circuit emulation of non-fixed instruction set VLSI devices
Description of the Prior Art
In the design of a computer system, development systems are used which allow the designer to develop and test programs and hardware systems. Typically, development systems include an in circuit emulator as a computer system design tool. In circuit emulation refers to the ability to replace a device in a system under test with a plug-in connector which is connected to an emulator which makes the plug-in connector appear to the system under test as nearly like the device which was removed as possible. In this way, the emulator or the target machine (the computer system under test) can have control of the device. When the emulator takes control of the device, it can interrogate to determine the state of the device, including reading the values of internal registers and stacks.
Currently, there are emulators in existence for most MOS microprocessors. All of these MOS microprocessors are fixed instruction set machines. This means that the microprocessor has an instruction set built into it. However, there is no emulator support for non-fixed instruction set devices. The term "non-fixed instruction set devices" as it is used herein refers to VLSI devices which are used in machines (computers) where the designer selects the instruction set as opposed to the typical MOS microprocessor where the instruction set is already chosen. Examples of such devices include the 29116 and 2910 devices manufactured by Advanced Micro Devices. While it is understood that 29116, 2910 and other similar devices do have a fixed set of operations they will perform, the terminology regarding a "non-fixed instruction set" used herein was selected to differentiate devices such as the 29116 and 2910 from MOS microprocessors. Included within the various categories of non-fixed instruction set devices are those referred to as bit slice microprogrammable parts. In general, the prior art has not been able to emulate microprogrammed VLSI devices for use in a development system. VLSI refers to Very Large Scale Integration. Integrated circuits utilizing VLSI technology are generally characterized by putting an entire function on a large integrated circuit, packaging it and utilizing that function as a subsystem in an overall circuit. VLSI implementation may be in the form of a complete microprocessor, but may also be in the form of gate-arrays, custom circuits or semi-custom circuits. It has only been within the last few years that the semiconductor industry has had the capability to implement VLSI. As VLSI development continues, the need for emulator support for non-fixed instruction set VLSI devices will increase.
It is desirable to record events occurring within the device, such recording capability is called the "trace". It is therefore desireable to provide a means for connecting the various input/outputs and control signals of the device to a trace.
Currently, emulator controllers are capable of controlling only one emulator head. It is desirable to have an emulator controller control more than one emulator head at a time.